A single DEA agent is responsible for ending Methaqualone's status as a prescription drug, and thus single handedly stopped the major Quualude abuse epidemic. He still works for the DEA, Rolling Stone mentioned him in a recent article about the Methamphetamine problem today. He wants to do to PseudoEphedrine what he did with Methaqualone.
It has medicinal value; just like Glutethimide, Ethchlorvynol, Pentobarbital, etc
It was controlled due to disproportionate amounts of recreational abuse, and lots, and lots of overdoses, suicides, rape's, etc involving it.
Following its change to CI, there was a lot of clandestine Methaqualone labs around the country making it (Rhodium and co. still host workups). Then everyone decided to just make Diazepam tablets and call them Quualudes, and by then everyone in the US moved on to new drug fads.